One example of prior-art rotary type bag filling apparatus is described in U.S. Pat. No. 3,982,376, wherein a multiplicity of clamps arranged equidistantly on an endless chain are moved in circulation integrally with the chain along an elliptic path so that while the clamps are advanced at one-pitch intervals on the elliptic path, bags are sequentially supplied to the clamps, are opened wide at the mouth while being suspended from the respective clamps, and are then filled with a product; thereafter heat is applied to seal the mouth of each filled bag, and at a terminal station of the process, the bags are successively released from the clamps. Another arrangement is disclosed in U.S. Pat. No. 4,534,158, wherein a large number of clamps are arranged around the peripheral edge of a disc in equally spaced relation and adapted to be advanced integrally with the disc at one-pitch intervals, so that a similar type of operation is carried out during one cycle of movement of the clamps around the circular path. Known bag filling apparatuses of the above described type have a common advantage that they are very efficient in that packaged products are mechanically turned out at exactly same intervals as the feed pitch of the clamps.
With these prior art apparatuses, however, one problem is that, as often encountered with automatic product filling machines, when the product storage tank has become empty, the emptiness remains unnoticed for some time so that empty bags suspended from the clamps successively pass beneath the filling hopper without being filled. In manual mode filling operation in which product filling is manually carried out, it may sometimes happen that some bags are inadvertently skipped and passed without being filled. In the prior art arrangement, no preventive measure is taken against such filling failure, and therefore, empty bags, if any, remaining as such will be sealed at the mouth in same way as filled bags. The sealed empty bags cannot be recycled. This is very uneconomical. At the operating location where filled bags are released from the clamps, empty or unfilled bags, if any, may fly in the air when released from the clamps.